Along with the advancement of IT and the spreading of the Internet, the amount of data handled by computer systems in companies and the like is continuously increasing. Therefore, in many computer systems, a storage apparatus (storage system) for storing a large amount of data is provided separately from a built-in storage apparatus of the host computer, adopting a configuration where the respective host computers and the storage system are mutually connected via a device-sharing network such as a SAN (Storage Area Network). Most of the data handled by the respective host computers is stored in the storage system, and the respective host computers access volumes (logical units) provided by the storage system. Such configuration is advantageous in that when replacement of the host computer becomes necessary, the physical movement or replication of the data from a host computer prior to replacing the data (migration source host) to a host computer after replacing the data (migration destination host) is not required, and only a simple operation of connecting the migration destination host to the network and performing setting of the volumes of the storage system used by the migration source host to enable access thereof from the migration destination host is required.
Further, in a computer system handling important data, a configuration is often adopted where many components are duplicated to prevent the occurrence of system stop or the like caused by failure of devices and components. The transmission line (transmission path) connecting the host computers and the storage system is also duplicated, and in many cases, the path connecting the host computers and the volumes of the storage system are duplicated or multiplexed, so that a system is constructed where the remaining paths can be used to continue operation even when failure such as disconnection occurs to a single path. However, in such configuration where multiple paths connecting the volumes of the storage system exist, a single volume within the storage system may seem like multiple volumes to the host computer, so that in order to solve this problem, many host computers adopt a software called an alternate path software in which the multiple volumes visible to the host computer are virtualized as a single volume, and when failure such as disconnection of a path occurs, that failure will not be visible from the host computer. For example, patent literature 1 discloses an art of having a server mounting an HBA (Host Bus Adaptor) where volumes provided from two storage systems are recognized as a single virtual volume.